Chemical sensors are of great importance in health care, industrial processing, environmental monitoring and remediation, energy production, and national defense. The ideal chemical sensor would have one or more of the following characteristics: (1) fast response, (2) high sensitivity, (3) high selectivity, (4) capability of detecting and recognizing as many chemicals as possible, (5) low power consumption (e.g., not relying on ionization or vaporization) and (6) small, lightweight, compact, (7) easy to use, and (8) inexpensive. Achieving these characteristics, however, has been challenging in previous sensor applications, with no single sensor having all of these characteristics. While great strides have been made in sensor technology over recent years, many sensors are still too large, unreliable, and expensive for widespread and easy use. For example, mass spectrometry, which is both highly sensitive and highly selective, typically requires vacuum equipment, resulting in sensors which are not compact and have high power consumption. In contrast, inexpensive and easy to use sensors, such as in-home carbon-monoxide detectors, typically are limited to detecting only one or two chemical species.